Start Game from File, how to send a message
You can't send anything from a blend file. A blend file is just a container for data. It gets read and written by Blender. The BGE can read them (but does not write to it).
Game Sessions
As you are talking about blend files I guess you mean game session (you are using the game actuator to switch levels). A game session is when you start your game and lives until it ends (quit). When you start again, you get a new session without any relationship to a previous one. Game sessions can run parallel. They still have no relationship to each other.
What you need is to transfer game status between game sessions.
Parallel
When two game sessions are running at the same time they can communicate via network (Python -&gt; socket). In this case I suggest to search for question/answer regarding network communication. Be aware this is no topic for beginners.
Sequential
When two game sessions are not running at the same time you need to persist the game status. Persistence between game sessions can be in the file system (or a database) -&gt; It must survive the end of the game session.
Therefore I suggest you specifically look for a question/answer dealing with Save/Load. This requires a bit of Python knowledge, but there are quite a few tutorials out there.
Levels as Scenes
When your levels are different scenes within the same game session, you could transfer game data via Messages or via Python. This is the case when you use the scene actuator.
Sorry but I can't give you a better answer with the information I currently have.
I hope it helps anyway